Recent microweathering phenomena in southern and central Sweden

More than 200 weathering sites, in southern and central Sweden, representing different rock types and environments have been investigated. Field studies were complemented by thin-section examination and laboratory simulation experiments. Research results in a classification of weathering forms in crystalline rocks in cool temperate climates. Special attention is paid to Holocene microweathering, facilitated because glaciation removed most old weathered material. Only minor forms, including surface colorations, mineral weathering, pitting and flaking, have been produced entirely during the Holocene. Where recent breakdown is observed, the primary reason must be sought in the geological history of rock. Holocene microweathering a few cm in depth is caused by a complex interaction between different weathering processes. Salt crystallization, however, seems important in areas that have experienced seashore conditions. Often the forms produced are as much the result of rock properties as of actual weathering processes. L'alteration a ete etudiee en Suede centrale et meridionale en plus de 200 sites representant differents types de roches et d'environnements. Les etudes de terrain ont ete completees par l'examen de sections fines et par des experiences de simulation en laboratoire. Cette recherche conduit a proposer une classification des formes d'alteration dans les roches cristallines sous des climats temperes froids. Une attention speciale est accordee a la micro-alteration dont l'etude des actions holocenes a ete facilitee par le fait que la glaciation a emporte la majorite du vieux materiel altere. Seules, des formes mineures comprenant des colorations de surface, l'apparition de petites cavites et l'ecaillage dans des mineraux paraissent devoir ětre entierement formees pendant l'Holocene. Quand une rupture recente de la roche est observee, la raison premiere doit ětre cherchee dans l'histoire geologique de la roche. Une micro-alteration holocene de quelques mm de profondeur est due a une interaction complexe entre differents processus d'alteration. L'action de cristallisation des sels semble toutefois importante dans les sites qui ont ete exposes a des conditions littorales. Souvent les formes produites resultent a la fois des proprietes de la roche et des processus d'alteration actuels.